Glider angle of attack indicator by SafeFlight

Eric Greenwell a écrit :

Does anyone know of documentation that supports the idea showing the
pilot the AOA will actually improve a glider pilot's thermalling? Or
even that the range of AOA needed to be "efficient" is too small for a
pilot to obtain it easily by using airspeed, or by just looking out the
canopy, once he's flown the glider enough to be familiar with it?

Hi Eric,

Optimum thermalling implies flying near minimum turn radius, thus near Clmax.
Modern profiles (beginning at Discus or ASW 24) have flat Cl curves in order to
be less sensitive to stall. Thus you can fly a little beyond maximum lift
without stalling or even "feel bad". That means that at 2 differents AOA (each
side of ClMax AOA) you have the same lift (Cl) thus the same airspeed !

Therefore it is absolutely *impossible* to use airspeed as a mean to control AOA
(even let away the influence of load, bank, bugs, etc.) in that range, as you
might do in approach, at smaller AOAs.

The only difference is the drag (thus the sink rate), which will be
significantly increased beyond the ClMax AOA. There may be a very light
buffeting noise and/or feeling but you will not be aware of it if you don't pay
a very close attention to it.

Try a piece of wool on the side of your canopy as an AOA indicator, as already
suggested, and you will be convinced. Put both of them each side to see the
influence of yaw if you wish. Get a pencil and a tape on the inner side of the
canopy to mark AOAs. The best way is to try first in straight flight, and look
for AOA that gives you minimum speed (better use GPS speed than pneumatic speed,
since the latter is getting pessimistic at high AOAs due to pitot masking). That
will be the AOA-to-fly for best climb. Then continue to put the stick back and
watch the AOA. There should be a noticeable AOA range whithout significant speed
change nor near-stall warnings. Then do the same in steady turning flight: it
should not change a lot except for higher speeds and yaw influence. You may try
different flap settings also.

I did first this experiment when I began to fly Crystal (a glider with a profile
similar to the Discus) in which it made a dramatic climb improvment not to fly
at too high AOAs. I tried it also in my ASH 26, as I would in any new glider
until I get accustomed to it (I don't need using it after a while, though I
would if a better AOA indicator was available).

Denis

BTW: yes you can "see" AOA - at least in no headwind - it's the angle between
the nose of your glider and the point of the ground you are aiming for in final
approach... it's not easy to convert that into degrees, but who cares ? What
matters is to get used to it

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